protactinium

[ proh-tak-tin-ee-uhm ]

noun

, Chemistry.

1. a radioactive, metallic element. : Pa; : 91.

protactinium

/ ˌprəʊtækˈtɪnɪəm /

noun

1. a toxic radioactive metallic element that occurs in uranium ores and is produced by neutron irradiation of thorium. Symbol: Pa; atomic no: 91; half-life of the most stable isotope, ²³¹Pa: 32 500 years; valency: 4 or 5; relative density: 15.37 (calc.); melting pt: 1572°C Former nameprotoactinium

protactinium

/ prō′tăk-tĭn′ē-əm /

1. A rare, extremely toxic, radioactive metallic element of the actinide series that occurs in uranium ores. It has 13 known isotopes, the most stable of which is protactinium 231 with a half-life of 32,760 years. Atomic number 91; approximate melting point 1,550°C; specific gravity 15.37; valence 4, 5.
2. See Periodic Table

Word History and Origins

Origin of protactinium¹

First recorded in 1915–20; prot- + actinium